Long-term expansion and maintenance of cord blood haematopoietic stem cells using thrombopoietin, Flt3-ligand, interleukin (IL)-6 and IL-11 in a serum-free and stroma-free culture system.

Although cord blood (CB) compares favourably with other haematopoietic stem cell (HSCs) sources, its use in large patients is limited by the low number of cells available. Ex vivo expansion of CB HSCs has been used to overcome this limitation. In this study, we investigated the effect of different cytokine cocktails, including interleukin (IL)-6, IL-11, Flt3-ligand (FL) and thrombopoietin (TPO) combined with serum or serum-free medium on the ex vivo expansion of CD34+ cells from CB. Initial experiments showed that expansion could be slightly improved using serum, but we chose to use serum-free medium in the subsequent investigations to apply good medical practice (GMP) conditions suitable for clinical use. The highest expansion of CD34+ cells was obtained with a cocktail containing FL + TPO + IL-6 + IL-11. The median (range) fold expansions of CD34+ cells at 5 and 10 weeks with serum-free medium were 235.6 (131.3-340) and 5205.6 (4736.6-5674.7) respectively. The absence of IL-11 was associated with a similar fold expansion after 5 weeks (median 215.6, range 149.8-281.5), but after 10 weeks expansion was slightly lower (median 1314.7, range 645-1984.4). Our data support the possibility of maintaining long-term expansion of CB HSCs in a simple stroma- and serum-free system.